I think bounty award is only one time process we can not move it among answer like we do while accepting an answer. In simple word we can not award the same bounty again in question.
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Harry JoyJun 1 '11 at 8:55

@Harry - I think you can move bounties just as you can move answers too unless some new change has been done in this regard.
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Sachin ShanbhagJun 1 '11 at 8:59